Lab #7
Estimating Abundance –Mark and Recapture
(1). I have decided to do a population study of black bears in Pennsylvania. I, along with
my colleagues captured and tagged bears in two discrete locations within close proximity
to two check stations. I am assuming that I can use a Lincoln-Petersen estimation
procedure because these bears do not roam outside of a fixed home range. Ultimately I
want to comment on the abundance of bears in each respective area. I met all
assumptions for the estimator and assume that both populations are isolated from one
another, i.e., there is no emigration or immigration because of their non-overlapping
home ranges. Compute an estimate of population size for both populations and their
respective 95% confidence intervals. Which confidence interval estimator did you
select? Why? Which population estimate do you think is better? Why? Which formulas
you elected to use for the confidence interval estimates?
Population 1: M = 158, C = 62, R = 22
Population 2: M = 312, C = 158, R = 9
(2). The following data were collected from marked and released sunfish in an Indiana
lake for 14 days. Fill in the column marked Mt. Calculate an estimate for the population
size and a 95% confidence interval using the Schnabel estimator.
t
Ct
Rt
new marked Mt
1
10
0
10
2
47
0
47
3
27
0
27
4
8
0
8
5
5
0
5
6
4
0
4
7
6
2
4
8
15
1
14
9
10
5
5
10
17
5
12
11
14
4
10
12
5
2
3
13
15
2
13
14
19
3
na
totals
0
Lab #7
(3). What are the assumptions of the Lincoln-Petersen and Schnabel population
estimators? Describe three situations in wildlife or fisheries where you might be able to
use either of these estimators. Explain how you would satisfy each assumption in each
situation.
(4). The following Method B table was computed by Leslie et al. (1953) for field voles in
Wales. Remember that for sample 1 you will have no population estimate and for the last
sample, you will have no estimate for the size of the marked population or the population
size.
Leslie, P.H., D. Chitty, and H. Chitty. 1953. The estimation of population parameters
from data obtained by means of capture-recapture method III. An example of the
practical application of the method. Biometrika 40:137-169.

mt = number of marked animals caught in sample t

ut = number unmarked animals caught in sample t

nt = number of animals caught in sample t, mt + ut

st = number of animals released after sample t (nt - # of accidental deaths)

mrt = number of marked animals caught in sample t, last caught in sample r

Rt = number of the st individuals released at sample t and caught again in a later
sample

Zt = number of individuals marked before sample t, not caught in sample t, but
caught in some sample after t.
Lab #7
1. Estimate the population size at time interval. To estimate the population size, use the
following equations:
A. Proportion of animals marked at time t.
B. The number of marked animals in the population.
C. The population estimate (FILL IN THE TABLE – I GOT YOU STARTED).
2. Estimate the survival rate at each interval.
3. Estimate the dilution rate at each interval. (Add a column to your table)
Time of capture, t
1
2
3
4
5
6
7
8
9
10
11
12
13
mt
0
12
17
23
20
28
57
49
57
44
62
82
19
st
96
41
82
64
64
104
121
89
92
95
127
188
25
nt
107
45
85
69
67
106
125
99
117
98
127
190
26
Rt Zt alphat Mt Nt Φt
25 0 N/A N/A N/A
11 13
34 7
na na
na
na
λt
na
4. Plot your results for Nt against time and plot Φt against λt. What do these graphs tell
you?
5. Based on your findings in the above table, what can you conclude about this
population of field voles?
6. What are the assumptions of the Jolly-Seber population estimation procedure?